1. Field of the Invention
This invention relates to syringes, and more particularly, to syringes having a protector cap mounted on a tip portion formed integral with a syringe cylinder.
2. Description of Prior art
Syringes often have a protector cap mounted on the tip portion of the syringe cylinder. Prior art protector caps are provided on the inner surface with projections for engaging the outer surface of the tip portion to facilitate mounting of the protector cap. The interior of the protector cap is thus sealed from the outside, escaping full sterilization when the syringe is enclosed in a package and gas-sterilized.
One common attempt to eliminate this shortcoming has been to provide the tip portion with a plurality of axially extending ribs to contact the inner surface of the protector cap. The protector cap has a step formed at a given position on the inner surface, which abuts the front ends of the ribs to stop at this position the advance of the tip portion into the protector cap during engagement of the cap. These ribs permit the interior of the protector cap to communicate with the cap exterior to allow for gas sterilization.
Since the protector cap is positioned relative to the tip portion through the abutment of the rib front ends with the protector cap inner step, the ribs and the step must be somewhat increased in width or height, resulting in an undesirable increase in the size of the protector cap. A small protector cap requires the tip portion to be of relatively small diameter, which in turn, necessitates high precision in embedding a cannula in the tip portion, resulting in a reduced yield of production. A small diameter tip portion has the associated danger that the cannula will pierce the protector wall partly because a cannula of small diameter is likely to bend and partly because such a cannula is difficult to embed perpendicularly in the tip portion. It is also difficult to firmly engage the protector cap on the tip portion because of its small size. There remains in addition the possibility that the tip portion of the cylinder may be moved beyond the step on the protector cap inner surface by any extra force to bring the protector cap rear end in sealing contact with the cylinder front end. Such sealing is undesirable for effective gas sterilization.